The explosion of the Internet and the desire to provide multiple communications and entertainment services to end users have created a need for a broadband network architecture that improves access to end users. Although the bandwidth of backbone networks has experienced a substantial growth in recent years, the bandwidth provided by access networks has remained relatively unchanged. Thus, the “last mile” still remains a bottleneck between a high capacity LAN or Home network and the backbone network infrastructure.
Digital Subscriber Line (DSL) and Cable Modem (CM) technologies offer some improvements over more conventional last mile solutions. However, these technologies still do not provide enough bandwidth to support emerging services such as Video-On-Demand (VoD) or two-way video conferencing. In addition, not all customers can be covered by DSL and CM technologies due to distance limitations.
One broadband access network architecture that offers a solution to the “last mile” problem is a point-to-multipoint passive optical network (PON). A point-to-multipoint PON is an optical access network architecture that facilitates broadband communications between an optical line terminal (OLT) and multiple remote optical network units (ONUs) over a purely passive optical distribution network. A point-to-multipoint PON utilizes passive fiber optic splitters and combiners to passively distribute optical signals between the OLT and the remote ONUs.
In the past, much of the PON development has been focused on ATM-based PONs. However, in recent years, there has been a growing interest in Ethernet-based PONs. This growing interest is partly due to the fact that about ninety-five percent (95%) of LANs currently use the Ethernet protocol. Therefore, Ethernet-based PONs are much more preferable than ATM-based PONs to interconnect Ethernet networks. Another contributing factor is that Ethernet is more compatible with the IP protocol, which is the protocol for the Internet.
However, unlike ATM, Ethernet was not originally designed to provide synchronization of telecom clocks to facilitate proper voice transmission through an Ethernet-based network. Therefore, in an Ethernet-based PON, synchronized telecom clocks may have to be independently extracted by the OLT and the ONUs from one or more external sources, such as central offices. Alternatively, a telecom clock may have to be distributed from a single source, such as the OLT, to the rest of the network, e.g., the ONUs, over a different transmission medium than the optical fibers that interconnect the OLT and the ONUs. However, these solutions significantly increase the overall cost of the PON components, as well as increase the complexity of the Ethernet-based PON.
In view of the above concern, there is a need for a system and method for economically and efficiently synchronizing telecom clocks throughout an Ethernet-based PON. In addition to PON applications, there is a need for system and method for economically and efficiently synchronizing telecom clocks across any unsynchronized point-to-point network connection.